Despite embattled Staten Island Rep. Michael Grimm’s insistence that “political” enemies tossed cement blocks through the windows of his campaign headquarters, a 14-year-old boy yesterday confessed that he and some buddies vandalized the storefront office as a prank last weekend, cops said.

But the middle-schooler’s admission to a guidance counselor left open the question of who — if anyone — wiped clean computer hard drives at Grimm’s headquarters, as the congressman claimed a day earlier of the break-in.

The freshman Republican congressman was quick to point fingers after the vandalism at his New Dorp headquarters was discovered Sunday.

Grimm — who is under federal criminal investigation over fund-raising for his 2010 campaign — called the window-breaking and computer-tampering “politically motivated crimes” and an “assault on democracy.”

“This was not a random act of vandalism by kids throwing rocks,” the former Marine and FBI agent insisted on Monday.

Cops were “very suspicious” about the combination of “brutal” window-smashing and “sophisticated” computer-tampering.

The unidentified teen will be charged with criminal mischief as a minor.

Grimm called the vandalism “unfortunate,” and then said, “We are very relieved to know this is not politically motivated.” He even invited the teen vandal to intern in his office.

“We still do not know what happened to the computers and are waiting for the NYPD computer-crimes unit to determine the nature of the tampering,” Grimm said. “It is possible that a volunteer could have inadvertently compromised the computer and failed to report it.”

A spokesman for Grimm’s Democratic challenger, Mark Murphy, said, “The wild accusations and apparently totally false conspiracy theories of the last 48 hours have made this bizarre situation a sad spectacle.

“It’s pretty clear at this point that Congressman Grimm is caving under the pressure of multiple ongoing investigations,” said Murphy’s spokesman, Nathan Smith.

Despite those questions, Grimm still leads Murphy by 48 percent to 38 percent among voters in their Staten Island-Brooklyn district, according to a Siena Research Institute poll released yesterday.